Method for optimizing response time of hydraulic latch-pin in cylinder deactivation rocker arm

ABSTRACT

A method for optimizing response time of a latch in a cylinder deactivation rocker arm assembly is provided. The latch is configured to move between an engaged position with an inner arm of the rocker arm assembly and a retracted position. A major outer diameter (L 1 ) of the latch is determined. An installed length (L 2 ) of a spring biasing the latch is determined. A clearance (L 3 ) between L 1  and a major inner diameter of an outer arm of the rocker arm assembly is determined. A radial clearance (L 4 ) between a cage coupled to the outer arm and a major inner diameter of the latch is determined. A minor diameter (L 5 ) of the latch is determined. A relationship between the response time of the latch and L 1,  L 2,  L 3,  L 4  and L 5  is established. Components of the cylinder deactivation rocker arm assembly are selected based on the relationship.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/US2014/053689 filed on Sep. 2, 2014, which claims the benefit of U.S. Provisional Patent Application No. 61/872,621 filed on Aug. 30, 2013, U.S. Provisional Patent Application No. 61/872,624 filed on Aug. 30, 2013 and U.S. Provisional Patent Application No. 61/898,475 filed on Nov. 1, 2013. The disclosures of the above applications are incorporated herein by reference.

FIELD

The present disclosure relates generally to switching roller finger followers and more specifically to methods for optimizing response times of a latch pin for a cylinder deactivation rocker arm.

BACKGROUND

A switching roller finger follower or switching rocker arm allows for control of valve actuation by alternating between two or more states, usually involving multiple arms, such as in inner arm and outer arm. Switching rocker arms can be used in variable valve actuation (WA) systems to improve engine fuel economy.

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named Inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

A method for optimizing response time of a latch in a cylinder deactivation rocker arm assembly is provided. The latch is configured to move between an engaged position with an inner arm of the rocker arm assembly and a retracted position. A major outer diameter (L1) of the latch is determined. An installed length (L2) of a spring biasing the latch is determined. A clearance (L3) between L1 and a major inner diameter of an outer arm of the rocker arm assembly is determined. A radial clearance (L4) between a cage coupled to the outer arm and a major inner diameter of the latch is determined. A minor diameter (L5) of the latch is determined. A relationship between the response time of the latch and L1, L2, L3, L4 and L5 is established. At least one of the L1, L2, L3, L4 and L5 impacts the response time more than a remainder of the L1, L2, L3, L4 and L5. Components of the cylinder deactivation rocker arm assembly are selected based on the relationship.

The response time can be an ON response time required for the latch to move from the inner arm and enable switching to a cylinder deactivation mode. In one example, L4 has a greater impact on response time than L1, L2 and L3. In another example, L5 has a greater impact on response time than L1, L2 and L3. In one example, the relationship is established by the following equation:

ON Response time (ms)=22.1431+1.2675*L1−1.28*L2−0.2625*L3−8.8762*L4+8.1951*L5+0.55*L1*L2−2.825*L1*L4−2.77*L1*L5+0.655*L2*L4−0.6050*L2*L5−0.4875*L3*L4−4.035*L4*L5.

In another example, the response time is an OFF response time required for the latch to move from the retracted position to the engaged position. L1 can have a greater impact on response time than L2, L3, L4 and L5. L4 can have a greater impact on response time than L2, L3 and L5. L5 can have a greater impact on response time than L2 and L3. In one example, the relationship is established by the following equation:

OFF Response time (ms)=19.731+15.8987*L1+1.17163*L2−1.53*L3−7.6401*L4−4.405*L5+1.3375*L1*L2−10.265*L1*L4−1.837*L1*L5−1.005*L2*L5+1.7875*L4*L5.

A method for optimizing ON and OFF response times of a latch in a cylinder deactivation rocker arm assembly according to another example of the present disclosure is provided. The latch moves between an engaged position with an inner arm of the rocker arm assembly and a retracted position. The method includes determining a major outer diameter (L1) of the latch. An installed length (L2) of a spring biasing the latch is determined. A clearance (L3) between L1 and a major inner diameter of an outer arm of the rocker arm of the rocker arm assembly is determined. A radial clearance (L4) between a cage coupled to the outer arm and a major inner diameter of the latch is determined. A minor diameter (L5) of the latch is determined. A relationship between response time of the latch and L1, L2, L3, L4 and L5 is established. Each of L1, L2 and L5 have inverse relationships with respect to ON response time and OFF response time. Components of the cylinder deactivation rocker arm assembly are selected based on the established relationship.

According to other features, the ON response time is required for the latch to move from the inner arm and enable switching to a cylinder deactivation mode. L4 can have a greater impact on response time than L1, L2 and L3. L5 can have a greater impact on response time than L1, L2 and L3. L5 can have a greater impact on response time than L1, L2 and L3. In one example, the ON Response time is established by the following equation:

ON Response time (ms)=22.1431+1.2675*L1−1.28*L2−0.2625*L3−8.8762*L4+8.1951*L5+0.55*L1*L2−2.825*L1*L4−2.77*L1*L5+0.655*L2*L4−0.6050*L2*L5−0.4875*L3*L4−4.035*L4*L5.

According to additional examples, the OFF response time is required for the latch to move from the retracted position to the engaged position. L1 can have a greater impact on response time than L2, L3, L4 and L5. L4 can have a greater impact on response time than L2, L3 and L5. L5 can have a greater impact on response time than L2 and L3. In one example, the OFF response time is established by the following equation:

OFF Response time (ms)=19.731+15.8987*L1+1.17163*L2−1.53*L3−7.6401*L4−4.405*L5+1.3375*L1*L2−10.265*L1*L4−1.837*L1*L5−1.005*L2*L5+1.7875*L4*L5.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a front perspective view of an exemplary switching rocker arm constructed in accordance to one example of the present disclosure;

FIG. 2 is a partial sectional view of a switching mechanism of the switching rocker arm of FIG. 1 and shown with the valve in lift mode with the latch engaged;

FIG. 3 is a partial sectional view of the switching rocker arm of FIG. 2 and shown with the valve in cylinder deactivation mode with the latch disengaged;

FIG. 4 is a partial cross-sectional view of the switching rocker arm of FIG. 1 and shown with the latch engaged with the inner arm;

FIG. 5 is a partial cross-sectional view of the switching rocker arm of FIG. 1 and shown with the latch in a retracted position and in contact with the cage;

FIG. 6A is a partial cross-sectional view of the switching rocker arm showing the latch moving from the engaged position to the retracted position;

FIG. 6B is an end view of the cage and latch of the switching rocker arm of FIG. 6A;

FIG. 7 is a free body diagram of the latch during motion toward the cage;

FIG. 8 is a free body diagram of the latch during motion away from the cage;

FIG. 9A is a partial cross-sectional view of the switching rocker arm of FIG. 1 according to an exemplary baseline design;

FIG. 9B is a cross-sectional view taken along line A-A of FIG. 9A;

FIG. 10A is a partial cross-sectional view of the switching rocker arm of FIG. 9A according to an exemplary optimized design;

FIG. 10B is ac cross-sectional view taken along line A-A of FIG. 10A,

FIG. 11 is a graph illustrating an effect of clearance on diameter (L3) between the latch and the outer arm;

FIG. 12 is a graph illustrating an effect of radial clearance (L4) between the latch and the cage; and

FIG. 13 is a graph illustrating an effect of contact length (L6) between the latch and the outer arm.

DETAILED DESCRIPTION

The following teachings are directed toward methods for optimizing response time of a latch in a switching rocker arm. Specifically, the following discussion provides methods of optimizing latch response time or the time for the latch to move such that the switching rocker arm can shift from lift mode to deactivation mode and vice-versa.

With initial reference to FIG. 1, an exemplary switching roller finger follower (SRFF) assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference 10. The SRFF assembly 10 can be a compact cam-driven single-lobe cylinder deactivation (CDA) switching rocker arm 12 installed on a piston-driven internal combustion engine, and actuated with the combination of a duel-feed hydraulic lash adjusters (DFHLA) 14 and oil control valves (OCV) 16. The SRFF assembly 10 can be engaged by a single lobe cam 20. The switching rocker arm 12 can include an inner arm 22, an outer arm 24. The default configuration is in the normal-lift (latched) position where the inner arm 22 and the outer arm 24 are locked together, causing an engine valve 26 to open and allowing the cylinder to operate as it would in a standard valvetrain. The DFHLA 14 has two oil ports. A lower oil port or lash compensator pressure port 28 provides lash compensation and is fed engine oil similar to a standard HLA. An upper oil port 30, referred as the switching pressure port, provides the conduit between controlled oil pressure from the OCV 16 and a latch 32 (FIG. 2). When the latch 32 is engaged, the inner arm 22 and the outer arm 24 operate together like a standard rocker arm to open the engine valve 26. In the no-lift (unlatched) position, the inner arm 22 and the outer arm 24 can move independently to enable cylinder deactivation.

With continued reference to FIG. 1 and additional reference to FIG. 2, additional features of the SRFF assembly 10 will be described. A pair of lost motion torsion springs 40 are incorporated to bias the position of the inner arm 22 so that it always maintains continuous contact with the camshaft lobe 20. The torsion springs 40 are secured to mounts located on the outer arm 24 by spring retainers 44. The lost motion torsion springs 40 require a higher preload than designs that use multiple lobes to facilitate continuous contact between the camshaft lobe 20 and an inner arm roller bearing 50. The engine valve 26 can include a valve seat 54 and a valve guide 56. A valve spring 58 can bias to valve seat 54 away from the outer arm 24.

The OHV 16 can be an electronically controlled ON/OFF valve that receives an electrical signal from an engine control unit (ECU) 70. Engine oil is supplied to the OCV 16. As noted above, the OCV 16 is hydraulically connected to the DFHLA 14. The inner arm 22 is pivotally coupled to the outer arm 24 at a pivot axle 76. The connection at the pivot axle 76 allows the inner arm 22 to swing in relation to the outer arm 24. The latch 32 is installed at the end pivot side of the outer arm 24, above the DFHLA 14, with a purpose of providing a secondary connection between the inner arm 22 and the outer 24. A latch compression spring 80 biases the latch 32 in the extended position engaging the inner arm 22. The latch compression spring 80 is captured at one end by the latch 32 and at the other end by a cage 82 which is permanently joined with the outer arm 24. The lost motion springs 40 maintain the camshaft lobe 20 in permanent contact with the roller bearing 50 located in the inner arm 22. The balance between the oil pressure in the switching pressure port and the force of the latch compression spring 80 is pushing the latch 32 to engage or disengage the inner arm 22 and the outer arm 24.

Exemplary operating modes for cylinder deactivation will be described. Lift mode can occur at engine speeds up to 7200 rpm and all operating temperatures. In the absence of an electrical signal to the OCV 16, the oil pressure in the switching port can be regulated to 0.2 bar to 0.4 bar. The latch 32 is in the extended position and engaged with the inner arm 22. Cylinder deactivation or no lift mode can be available on engine speeds up to 3500 rpm and oil temperatures of 20 degrees Celsius or higher. The no lift mode is triggered by an electric signal from the ECY 70 to the OCV 16, which increases the oil pressure in the switching pressure port above 2.0 bar. The increase in pressure retracts the latch 32 to disengage the inner arm 22. In one example oil pressure at 20 degrees Celsius is above 4.0 bar. Additionally, 2.0 bar oil pressure is practical at temperatures above 100 degrees Celsius. As a result, the oil pressure at cold temperature can be 3 bar.

With specific reference now to FIG. 2, a cross-section of the SRFF assembly 10 during lift mode will be described. In the absence of an electrical signal to the OCV 16, the oil pressure in the switching pressure port is 0.2 to 0.4 bar. The latch 32 is extended and engaged with the inner arm 22. The SRFF assembly 10 inner arm 22 and outer arm 24 are linked together working as a single body similar to a standard rocker arm. The camshaft rotational motion is transferred to the valve 26 through the inner arm 22 and the outer arm 24. The valve 26 opens and closes based on the lift profile of the camshaft lift lobe 20.

With specific reference now to FIG. 3, a cross-section of the SRFF assembly 10 during no-lift mode will be described. The electric signal from the ECU 70 energizes the OCV 16 to pressurize the switching port with engine oil pressure. In one configuration, a minimum of 2.0 bar is needed to overcome the latch spring 80 preload force, compressing the latch spring 80 and moving the latch 32 in the retracted position, disengaging the inner arm 22 from the outer arm 24. The SRFF assembly 10 can include a gap between the latch 32 and the inner arm 22 called latch lash. The lash allows the latch 32 to move in and out of the outer arm 24 based on the oil pressure in the switching port and when the camshaft is on the base circle. The absence of the connection between the latch 32 and the inner arm 22 results in camshaft rotational motion transfers to the inner arm 22 only that rotates around the pivot axle 76. Camshaft motion is not transferred to the valve 26 that remains at rest on the valve seat 54.

The CDA switching rocker arm 12 can enable switching from lift mode to deactivation mode and vice versa. Dual overhead cam engines have one OCV 16 that provides input to four SRFF assemblies 10 (two for intake valves and two for exhaust valves). The sequence of activating and deactivating the valves is important for proper function of the engine. The preferred sequence from switching from lift mode to deactivation is to deactivate the SRFF's connected to the exhaust valves first, entrapping the exhaust gas inside the cylinder, and then, deactivating the SRFF's connected to the intake valves. Switching from deactivation lift mode, the exhaust valves are activated first to relieve the pressure from the entrapped gas held in the cylinder during deactivation cycles. Next, the SRFF's connected to the intake valves are activated, allowing the intake valves to open at nearly atmospheric pressure. Exhaust gas being trapped inside the cylinder during the deactivation cycles is beneficial because it reduces the pumping loses and keeps the deactivated cylinder warm, maintaining the engine thermal efficiency. Switching between modes is required within one camshaft revolution and the sequence of switching the intake and exhaust is important and must be maintained for proper engine function. Exceeding the switching time for one of the SRFF can result in switching the SRFF in the wrong sequence.

The window available for switching is defined as the time that the hydraulic pressure can change modes and the latch mechanical movement can be complete to create the change from deactivation to activation and vice-versa. Mode switching occurs when the SRFF is on camshaft base circle condition when the latch 32 is under load from the inner arm 22 and can move freely.

Latch response time is defined as the time for the latch 32 to move such that the SRFF can shift from lift to deactivation mode and vice-versa. The time required for the latch 32 to move from the inner arm 22 and enable switching the SRFF to deactivation mode is referred to as “ON response”. The movement of the latch 32 is enabled by energizing the OCV 16. This increases the pressure in the switching pressure port to engine oil pressure. The increase in pressure overcomes the force in the latch spring 80 moving the latch 32 from the engaged to the retracted position.

Turning now to FIG. 4, the latch 32 is shown in the engaged position. The latch 32 is in the engaged position when the latch 32 front surface is in contact with the inner arm 22. The increase in the oil pressure in the switching pressure port moves the latch 32 a distance D1 from the engaged position to the retracted position. In the example shown the distance D1 can be 1.86 mm.

With reference now to FIG. 5, the latch 32 is shown in the retracted position. In the retracted position, the latch 32 is in contact with the cage 82. The latch 32 is completely inside the outer arm 24 and the connection between the inner arm 22 and the latch 32 is discontinued. The inner arm 22 remains free to pivot during the deactivation cycles. The OCV 16 is de-energized when no signal is sent to the OCV 16. The oil pressure in the switching pressure port is regulated to 0.2 bar to 0.4 bar. This pressure is insufficient to overcome the compressed spring force, moving the latch 32 to the extended position. The time for the latch 32 to travel from the retracted position to a partially engaged position is referred to herein as “OFF response”.

Referring now to FIGS. 6A and 6B, the latch 32 is shown in transit from the engaged position to the retracted position. FIG. 6A shows a cross-section along the axis of the latch travel. FIG. 6B represents a cross-section through a plane perpendicular to the direction of the latch movement. The oil residing between the latch inside pocket and the cage 82 creates a back pressure if the oil cannot quickly exit the SRFF through the hole located in the cage when the latch 32 moves to the disengaged position. An oil escape route 100 is formed between the latch 32 and the cage 82. The oil escape route 100 contributes to the ON response time reduction. As described herein, design changes to the interface between the latch 32 and the cage 82 were used to reduce the ON response time.

FIG. 7 illustrates a free body diagram of the latch 32 during motion toward the cage 82. The force that drives latch motion is the hydraulic force due to pressure from the OCV 16 at latch close end towards major outer diameter, F_(pa1). Forces that oppose latch motion are viscous friction due to fluid between the latch 32 and the outer arm 24, F_(viscous1) and F_(viscous2), the latch spring compression force, F_(spring), hydraulic force at latch close end toward minor diameter F_(pa2), and the hydraulic force acting on the latch 32 from the open end F_(pa3). The latch displacement, x is derived from Newton's second law of motion, with m being the latch mass identified in the following equation:

${m \cdot \frac{^{2}x}{t^{2}}} = {F_{{pa}\; 1} - F_{{pa}\; 2} - F_{{pa}\; 3} - F_{{viscous}\; 1} - F_{{viscous}\; 2} - F_{spring}}$

The oil pressure at switching port drops to 0.4 bar max when the OCV 16 is de-energized. The pressure is insufficient to overcome the compressed spring force, allowing the latch to move from the retracted position, where the latch 32 is in contact with the cage 82, away from the cage 82. FIG. 8 illustrates a free body diagram of the latch 32 during this motion wherein the forces that drive latch motion are the latch spring preload force, F_(spring), hydraulic force at latch close end towards minor OD, F_(pa2) and the hydraulic force acting on the latch 32 from the open end, F_(pa3). Forces that oppose the latch motion are fluid viscous friction on latch major and minor diameters F_(viscous1) and F_(viscous2), and hydraulic force due to oil pressure in the switching port F_(pa1). The latch motion moving away from the cage 82 as derived from Newton's second law is expressed in the following equation with x representing displacement and m representing the mass of the latch 32:

${m \cdot \frac{^{2}x}{t^{2}}} = {F_{spring} - F_{{pa}\; 1} + F_{{pa}\; 2} + F_{{pa}\; 3} - F_{{viscous}\; 1} - F_{{viscous}\; 2}}$

The methods according to the present disclosure identified various parameters that affect response time. FIGS. 9A and 10A illustrate cross-sections through the SRFF 12 in the direction of latch movement for a baseline design (FIG. 9A) and an optimized design (FIG. 10A). FIGS. 9B and 10B illustrate respective cross-sections perpendicular to the latch axis of movement with the latch 32 between the engaged and retracted positions. The following parameters were identified. A latch major outside diameter (OD) L1, an installed length L2 of the spring 80. A clearance between the latch major OD and the outer arm 24 bore major inside diameter (ID) L3. A radial clearance of the latch 32 to the cage 82, L4. A latch 32 minor OD L5. A contact length of the latch 32 to the outer arm 24, L6. A volume between the latch 32 and the cage 82, L7. The fluid escapes from the latch open end to outlet of the cage 82, exposed to cylinder head through the radial clearance L4.

The effects of latch major OD, L1 according to the present teachings will now be described. The ON response time reduces with increasing in latch major OD, L1 due to increases in the area available for pressure that results in hydraulic force F_(pa1). The OFF response time increases as diameter increases due to higher hydraulic force acting on the latch major OD, L1. A back pressure of 0.4 bar max is available in the switching pressure port during the latch motion from the disengaged position to the engaged position. Additionally, the rate at which the pressure in the switching port drops plays a role in the OFF response. The spring preload contributes effectively to the latch motion only after the pressure drops to a minimum pressure. Consequently before the pressure drops to minimum pressure, the dynamics of OCV interaction with latch and fluid path are important for accurate prediction of OFF response. The dynamics of OCV are influenced by latch major diameter, due to its frontal interaction.

The effects of spring installed length L2 according to the present teachings will now be described. The variation in spring load varies with L2. The installed length L2 affects the spring preload force. The larger the spring installed length, the lesser is the spring force. The ON response decreases with increase in installed length due to lower resistance offered by the spring during motion from the engaged position to the disengaged position. The OFF response decreases with lesser spring installed length, due to larger preload in the spring which is the driving force during motion from the disengaged position to the engaged position.

With reference to FIG. 11, the effects of the clearance on diameter L3 according to the present teachings will now be described. The clearance L3 between the latch major OD, L1 and the outer arm major ID affects the viscous friction force F_(viscous1) between the latch major OD and the outer arm major ID. The increase in clearance between the latch major OD, L1 and the outer arm major ID has an influence on the ON and the OFF response. The OFF response decrease with increase in clearance on the diameter L3, due to increased flow at the latch open end increasing pressure F_(pa3). The ON response decreases until the clearance reaches a predetermined distance such as 0.12 mm. The response time subsequently increases. In this regard, an increase in clearance up to 0.12 mm decreases viscous friction force and hence the ON response decreases. Beyond the 0.12 mm, the leakage is high and therefore very low hydraulic force acting on the latch major OD, L1, resulting in increased ON response.

With reference to FIG. 12, the effects of the radial clearance L4 according to the present teachings will now be described. The latch motion from engaged to retracted position disperses the oil on the volume cavity L7. The leakage flow starts from the clearance on the diameter L3, through the chamber volume L7 and exits the SRFF after passing through the radial clearance L4. FIG. 12 shows the effect of the radial clearance between the cage 82 and the latch major ID for ON and OFF response times. The ON time decreases with increases in the radial clearance because lesser opposing force F_(pa3) due to pressure generated at the cavity volume L7. With the increase in the clearance, the pressure in the cavity volume L7 drops, because the fluid is quickly exposed to atmospheric pressure through the opening in the cage 82. The OFF response follows similar physics in the latch motion during the return travel. The response of the OFF response is steeper compared to the ON response slope.

The effects of latch minor diameter L5 according to the present teachings will now be described. The ON response increases with increase in latch minor diameter L5 due to the relative increase in hydraulic force F_(pa2) compared to F_(pa1) which gives a resistive force for the retracted motion of the latch 32. The OFF response decreases with larger minor diameter due to combined effect of spring force F_(spring) and hydraulic force F_(pa2) acting in the same direction.

With additional reference to FIG. 13, the effects of contact length L6 according to the present teachings will now be described. ON and OFF response times are not significantly affected with the increase in contact length L6 between the latch 32 and the outer arm 24. The dependency of the contact length L6 to response time is shown in FIG. 13. The increase in contact length increases the friction forces. The change in contact length L6 and chamber volume L7 parameters do not affect the response times compared to other parameters.

According to the present methods, a quantitative transfer function yielding a relationship between control factors affecting output response is provided. Five control factors have influence on response time: latch major OD (L1), spring installed length (L2), clearance on diameter (L3), radial clearance (L4), and latch minor ID (L5). Transfer functions were developed from analyzing output results for ON and OFF response times. The effect of the factor is directly proportional to the magnitude of the associated coefficient. Higher magnitude of coefficient, the stronger the change in response. The coefficients of radial clearance (L4) and latch minor OD (L5) in the following equation show a strong influence and contribution of (−40%) and (+37%) respectively. This shows that moving the radial clearance (L4) to level 1 and keeping other factors at level 0 of non-dimensional values leads to a reduction of 40.0% ON response time or approximately 9 ms. The higher level interactions have negligible effect. The transfer functions were obtained for the non-dimensional value “0” and “+1” and are shown in the following equations for ON and OFF response:

ON Response (ms)=22.1431+1.2675*L1−1.28*L2−0.2625*L3−8.8762*L4+8.1951*L5+0.55*L1*L2−2.825*L1*L4−2.77*L1*L5+0.655*L2*L4−0.6050*L2*L5−0.4875*L3*L4−4.035*L4*L5

The coefficient of latch major OD (L1), radial clearance (L4), and latch minor OD (L5) in the OFF Response time equation (below) show a higher contribution of +81.0%, −39.0% and −22.0% respectively. This shows that moving the latch major OD (L1) to level 2 of non-dimensional values increases OFF response approximately 16 ms. The transfer function gives direction to move the radial clearance (L4) and latch minor OD (L5) to level 1 of non-dimensional value to reduce the OFF response time. The interaction coefficient of L1 and L4 show stronger contribution of 52.0% and indicates that to reduce OFF response, the latch major OD (L1) can move to level 1 of non-dimensional value with factor latch radial clearance L4. The remaining higher level interactions have negligible effect.

OFF Response (ms)=19.731+15.8987*L1+1.17163*L2−1.53*L3−7.6401*L4−4.405*L5+1.3375*L1*L2−10.265*L1*L4−1.837*L1*L5−1.005*L2*L5+1.7875*L4*L5

The latch major OD (L1), spring installed length (L2), latch minor OD (L5) are in inverse relationship with respect to ON and OFF response time. A response optimizer function was developed to understand the effect of different experimental settings on the ON and OFF response times with the purpose to explore sensitivity of ON and OFF responses with changes in the input variables. The function determines the best possible combination of the input variables, L1 to L5 that generated the shortest ON and OFF response time. The optimization objective was to minimize both response times and an arbitrary target of 12.0 ms was chosen to provide robustness to design variations. The two transfer functions derived earlier, an optimal combination of the design variables was found to minimize the ON and OFF response simultaneously. The following ideal dimensions were provided after optimization for the best ON and OFF response time. Latch major diameter L1=7.947 mm, spring installed length L2=7.126 mm, clearance between the latch major OD and outer arm bore L3=0.103 mm, radial clearance latch to cage L4=0.400 mm and latch minor OD L5=5.741. The design methods set forth herein move toward the level 1 for L2, L3 and L4 and level 0 for L1 and L5.

The optimized design is shown in FIGS. 10A and 10B where like reference numbers with an “A” suffix are used to denote like components. The optimized design includes changes to the latch 32A, the cage 82A and the spring installed length L2 to reduce the response time and balance the ON and OFF response. Optimized values were found for the factors L1 to L5. Packaging considerations restricted the changes of the latch major OD (L1) and the latch minor diameter (L5). The following design changes were made: L2 was decreased by 3.87% to balance the ON/OFF response. L3 was increased by 44% to reduce the viscous friction forces during latch movement and reduces both response times. L4 was increased by 53%. The optimized design modified the cage minor OD and increased latch ID. Further, as can be appreciated, the ON and OFF Response time equations provided by the instant methods can be used when selecting components of the SRFF assembly 10.

A plurality of different embodiments of the present disclosure is shown in the Figures of the application. Similar features are shown in the various embodiments of the present disclosure. Similar features have been numbered with a common reference numeral and have been differentiated by an alphabetic suffix. Also, to enhance consistency, the structures in any particular drawing share the same alphabetic suffix even if a particular feature is shown in less than all embodiments. Similar features can be structured similarly, operate similarly, and/or have the same function unless otherwise indicated by the drawings or this specification. Furthermore, particular features of one embodiment can replace corresponding features in another embodiment or can supplement other embodiments unless otherwise indicated by the drawings or this specification.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A method for optimizing response time of a latch in a cylinder deactivation rocker arm assembly, the latch moving between an engaged position with an inner arm of the rocker arm assembly and a retracted position, the method comprising: determining a major outer diameter (L1) of the latch; determining an installed length (L2) of a spring biasing the latch; determining a clearance (L3) between L1 and a major inner diameter of an outer arm of the rocker arm assembly; determining a radial clearance (L4) between a cage coupled to the outer arm and a major inner diameter of the latch; determining a minor diameter (L5) of the latch; establishing a relationship between the response time of the latch and, L1, L2, L3, L4 and L5, wherein at least one of the L1, L2, L3, L4 and L5 impacts the response time more than a remainder of the L1, L2, L3, L4 and L5; and selecting components of the cylinder deactivation rocker arm assembly based on the relationship.
 2. The method of claim 1 wherein the response time is an ON response time required for the latch to move from the inner arm and enable switching to a cylinder deactivation mode.
 3. The method of claim 2 wherein L4 has a greater impact on response time than L1, L2 and L3.
 4. The method of claim 3 wherein L5 has a greater impact on response time than L1, L2 and L3.
 5. The method of claim 4 wherein the relationship comprises: ON Response time (ms)=22.1431+1.2675*L1−1.28*L2−0.2625*L3−8.8762*L4+8.1951*L5+0.55*L1*L2−2.825*L1*L4−2.77*L1*L5+0.655*L2*L4−0.6050*L2*L5−0.4875*L3*L4−4.035*L4*L5.
 6. The method of claim 1 wherein the response time is an OFF response time required for the latch to move from the retracted position to the engaged position.
 7. The method of claim 6 wherein L1 has a greater impact on response time than L2, L3, L4 and L5.
 8. The method of claim 7 wherein L4 has a greater impact on response time than L2, L3 and L5.
 9. The method of claim 8 wherein L5 has a greater impact on response time than L2 and L3.
 10. The method of claim 9 wherein the relationship comprises: OFF Response time (ms)=19.731+15.8987*L1+1.17163*L2−1.53*L3−7.6401*L4−4.405*L5+1.3375*L1*L2−10.265*L1*L4−1.837*L1*L5−1.005*L2*L5+1.7875*L4*L5.
 11. A method for optimizing ON and OFF response times of a latch in a cylinder deactivation rocker arm assembly, the latch moving between an engaged position with an inner arm of the rocker arm assembly and a retracted position, the method comprising: determining a major outer diameter (L1) of the latch; determining an installed length (L2) of a spring biasing the latch; determining a clearance (L3) between L1 and a major inner diameter of an outer arm of the rocker arm assembly; determining a radial clearance (L4) between a cage coupled to the outer arm and a major inner diameter of the latch; determining a minor diameter (L5) of the latch; establishing a relationship between the response time of the latch and, L1, L2, L3, L4 and L5, wherein each of L1, L2 and L5 have inverse relationships with respect to ON response time and OFF response time; and selecting components of the cylinder deactivation rocker arm assembly based on the established relationship.
 12. The method of claim 11 wherein the ON response time is required for the latch to move from the inner arm and enable switching to a cylinder deactivation mode.
 13. The method of claim 12 wherein L4 has a greater impact on response time than L1, L2 and L3.
 14. The method of claim 13 wherein L5 has a greater impact on response time than L1, L2 and L3.
 15. The method of claim 14 wherein the ON response time comprises: ON Response time (ms)=22.1431+1.2675*L1−1.28*L2−0.2625*L3−8.8762*L4+8.1951*L5+0.55*L1*L2−2.825*L1*L4−2.77*L1*L5+0.655*L2*L4−0.6050*L2*L5−0.4875*L3*L4−4.035*L4*L5.
 16. The method of claim 11 wherein the OFF response time is required for the latch to move from the retracted position to the engaged position.
 17. The method of claim 16 wherein L1 has a greater impact on response time than L2, L3, L4 and L5.
 18. The method of claim 17 wherein L4 has a greater impact on response time than L2, L3 and L5.
 19. The method of claim 18 wherein L5 has a greater impact on response time than L2 and L3.
 20. The method of claim 19 wherein the OFF response time comprises: OFF Response time (ms)=19.731+15.8987*L1+1.17163*L2−1.53*L3−7.6401*L4−4.405*L5+1.3375*L1*L2−10.265*L1*L4−1.837*L1*L5−1.005*L2*L5+1.7875*L4*L5. 